An environmentally friendly vehicle such as an electric car, a hybrid car, and a fuel cell car promotes reduction in exhaust gas and improvement of fuel efficiency by using a motor as a driving source for driving a vehicle. In particular, a high voltage battery that is a power source for operating the motor is connected to the motor to be chargeable/dischargeable through an inverter. The high voltage battery of the environmentally friendly vehicle may have a battery pack structure in which a plurality of battery cells are disposed as one group to form a module and a plurality of battery modules are connected in series, to store and providing high-output and high-capacity electric energy.
Meanwhile, when the temperature of a battery module decreases in a cold weather condition, chargeable/dischargeable power may be reduced, and therefore, the efficiency of a battery system deteriorates. Accordingly, the temperature of a battery may be required to be increased to an optimal temperature or greater.
The capacity and output performance of the high voltage battery may deteriorate at substantially low temperatures or in the cold weather condition. Particularly, when the high voltage battery is used as a main power source in the electric vehicle, the electric vehicle may be substantially sensitive to the temperature of the battery, more so than the hybrid vehicle. Therefore, a battery heating system for raising the temperature of the battery within a reduced amount of time to increase the capacity and output of the battery at a vehicle start time may be required for the environmentally friendly vehicle. In addition, a battery heating system for raising the temperature of the battery to an optimal temperature may be required to charge the environmentally friendly vehicle in a reduced amount of time.
As an example of the related art for raising the temperature of the battery, a method for controlling heating of a high voltage battery has been developed. The method increases the temperature of battery modules using a balancing resistor. In addition, a heating apparatus of a battery module has been developed in the related art, and the apparatus may include a heater member having a heating wire to a side of a battery module.
For example, FIG. 1 illustrates a battery heating system in the related art. As shown in FIG. 1, a pad-type resistance heater such as a PTC planar heater 12 is installed to increase temperature in each battery module 11 constituting a battery pack 10. In particular, the resistance heaters 12 of the battery modules 11 are connected in series to be connected to the battery pack 10 through a heater relay 25. As such, as the on/off state of the heater relay 25 is controlled, the on/off state of all the resistance heaters 12 may be collectively controlled.
For example, the resistance heaters 12 are operated by receiving power supplied from the battery pack 10. Accordingly, when the heater relay 25 is switched to be the on state by a control signal of a battery management system (BMS) 30, all the resistance heaters 12 generate heat together as the power of the battery pack 10 is simultaneously supplied to the resistance heaters 12 of the battery modules 11, thereby simultaneously increasing the temperature of all the battery modules 11.
Particularly, the BMS 30 collects battery state information including the voltage current, temperature, state of charge (SOC) and the like of the battery pack 10, and directly uses the collected battery state information in charging/discharging control or provides the collected battery state information to other controllers inside/outside a vehicle to be used in vehicle control and the like.
In addition, a power relay assembly (PRA) 20 includes a plurality of high voltage relays for selectively opening/closing (+) and (−) power lines connected to the battery pack 10. The on/off state of each high voltage relay is controlled by the BMS 30. In particular, the PRA 20 includes two high voltage main relays that are main power contact points, i.e., a main relay ((+) main relay) 21 of the (+) power line and a main relay ((−) main relay) 22 of the (−) power line, and a precharge relay 23 and a precharge resistor 24, which are disposed on a circuit bypassing the main relay 21 of the (+) power line.
Meanwhile, the high voltage relays 21, 22, 23 and 25 described above may have a problem of welding, and hence an algorithm for determining the welding of these relays may be applied. When welding occurs in the relay, high voltage may be exposed to the exterior even in an IG-OFF state such as a parking state, and thus, a dangerous situation such as an electric shock may occur. The welding of the relay refers to a state in which two contact points are adhered by an arc generated between the contact points such that the on/off state of the relay may not be controlled. When the off state of the relays 21, 22, 23 and 25 is not possible due to the contact point welding, direct current (DC) high voltage may be exposed to the exterior, and thus, a dangerous situation such as an electric shock of a human body may occur. Accordingly, welding of high voltage relays including the heater relay 25 and the like in required to be checked as well as the main relays 21 and 22 of the (+) and (−) power lines and the precharge relay 23.
In the related art, a separate sensing circuit configured to sense voltage for each battery cell or battery module has been used to check welding. For example, the BMS 30 detects welding of the main relays 21 and 22, the precharge relay 23 and the like from the voltage sensed in the state in which the on/off state of each relay is controlled. A fault or failure of the battery heating system such as welding of the heater relay 25, is detected from a temperature of the battery module 11 or the resistance heater 12, sensed after the main relays 21 and 22 are on. Particularly, a temperature sensor configured to detect a temperature of the resistance heater is used as shown in FIG. 2.
For example, when the temperature of the resistance heater which is sensed by the temperature sensor increases in a state in which the off state of the heater relay 25 is controlled after the main relays 21 and 22 are on, the heater relay is determined to be in a welding state. In addition, whether temperature increases from a temperature of the battery module 11 or the resistance heater 12 which is measured by an individual temperature sensor is determined to detect a fault of the battery heating system such as a disconnection or short circuit of the resistance heater.
For example, when a variation in temperature between the battery modules 11 or a variation in temperature between the heaters is substantial in a state in which the temperature of the battery module 11 increases to an extent after the heater relay 25 is the on state, the heater is determined to be short circuited. When the temperature of a specific battery module 11 or the temperature of a specific heater does not increase even when the heater relay 25 is a on state, the corresponding resistance heater 12 is determined to be disconnected or a heating wired is disconnected.
However, in the related art, a temperature sensor is required for each battery module 11 or the resistance heater 12 separately from the voltage sensing circuit for detecting welding of the relay (FIG. 2) in order to detect a fault of the battery heating system. Moreover, when a fault of the battery heating system is detected by identifying a variation in temperature between the battery modules in the state in which the temperature of the battery module is raised to an extent, such as detection of a short circuit of the heater, or by identifying an increase in temperature after the heater relay is the on state, such as detection of a disconnection of the heater, time to identify a variation in temperature or an increase in temperature may increase.
Accordingly, misdiagnosis may occur due to an environment such as external air or a system characteristic. For example, a variation in temperature may occur due to the influence of a flow path and the like during the operation of a fan and an increase in temperature may occur due to the use of a battery. Hence, the clear decision with respect to a faulty part may not be possible due to the environment and the system characteristic.
The above information disclosed in this section is merely for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.